CIRCULATION OF BLOOD. 3a 
rounded edges, but no nuclei. Note the tendency 
of the red corpuscles to run together into 
rouleaux, like piles of coins. Average diameter 
about zs'5> of an inch. 
ii, White corpuscles: much as in frog: slightly 
larger than the red corpuscles, averaging about 
zeoo Of an inch in diameter; amceboid move- 
ments not well seen unless the slide is warmed. 
2. Action of acetic acid, 
Treat with acetic acid as before: note that unlike the frog’s 
no nuclei are visible in the red corpuscles. 
F, Circulation of the Blood in the Web of a Frog’s Foot. 
The Web uniting together the toes of the frog’s foot is so 
thin and transparent, that with the microscope the blood can 
readily be seen coursing along the capillaries. 
Lxamine a frog prepared to show the circulation in the web of 
the foot. Note: 
1. With a low power : 
a. The irregularly branched pigment cells to which the 
colour of the frog’s skin is due. 
b. The fine meshwork of bloodvessels along which the 
blood can be seen flowing. ‘These bloodvessels are 
of three kinds :-— 
i. The arteries: carrying blood to the web: distin- 
guished by the fact that when they divide the 
direction of flow of the blood is from the larger 
trunk to its branches. 
ii. The capillaries: a close network of very small, 
very thin-walled vessels, along which the blood 
flows from the arteries to the veins. 
iii, The veins: carrying the blood away from the web 
back towards the heart: distinguished from 
arteries by the fact that the blood flows from 
smaller to larger vessels. 
2 With a high power: note the following points : 
a. The walls of the arteries and veins ; much thicker than 
C 
